The present invention relates to stable, non-hygroscopic salts of L-carnitine and lower alkanoyl L-carnitine endowed with enhanced nutritional and/or therapeutical efficacy with respect to their inner salts congeners and to solid compositions containing such salts, particularly suited to oral administration.
It has long since known that carnitine and its alkanoyl derivatives lend themselves to various therapeutical utilizations such as e.g. in the cardiovascular field for the treatment of acute and chronic myocardial ischaemia, angina pectoris, heart failure and cardiac arrhythmias. Acetyl L-carnitine is used in the neurologic field for the treatment of both central nervous system disturbances and peripheral neuropathies, particularly diabetic peripheral neuropathy. Propionyl L-carnitine is used for the treatment of chronic arteriosclerosis obliterans, particularly in patients showing the symptom of severely disabling intermittent claudication.
On the other hand, a widespread promotion of carnitine and derivatives thereof has rapidly been taking place towards utilizations other than those purely therapeutical, ever though allied to them.
It has, in fact, been widely recognized that in professional athletes as well as in any subject practising sport at amateur level, L-carnitine supplies energy to the skeletal musculature and increases the resistance to prolonged, intense stress, enhancing the performance capability of such individuals.
In addition, L(xe2x88x92)-carnitine or its lower alkanoyl derivatives constitute indispensable nutritional supplements for both vegetarians, whose diets have a low carnitine content as well as a low content of the two amino acids, lysine and methionine (the precursors of the biosynthesis of L(xe2x88x92)-carnitine in the kidneys and liver) and those subjects who have to live on a diet poor in protein for prolonged periods of time.
Consequently, various compositions containing carnitine or derivatives thereof, either as single components or in combinations with further active ingredients, have recently reached the market of the dietary supplements, health foods, energy foods and similar products.
It has long since been known that L(xe2x88x92)-carnitine and its alkanoyl derivatives are extremely hygroscopic and not very stable when they occur as inner salts (or xe2x80x9cbetainesxe2x80x9d) as represented by the formula 
wherein Rxe2x95x90H or C1-C5 lower alkanoyl.
This leads to complex problems of processing, stability and storage both of the raw materials and of the finished products. For example, L(xe2x88x92)-carnitine tablets have to be packaged in blisters to keep them out of contact with the air, since, otherwise, even in the presence of normal humidity conditions, they would undergo alterations, swelling up and becoming pasty and sticky.
Since the salts of L(xe2x88x92)-carnitine and its alkanoyl derivatives known to-date present the same therapeutic, nutritional or dietetic activities, respectively, as the so-called inner salts (or xe2x80x9cbetainesxe2x80x9d), the problem of the hygroscopicity of the inner salts has tentatively been solved by salifying them with xe2x80x9cpharmacologically acceptablexe2x80x9d acids, which do not present unwanted toxic or side effects.
There is now an extensive body of literature, particularly patents, disclosing the production of such stable, non-hygroscopic salts.
Among L-carnitine salts, particularly L-carnitine tartrate and L-carnitine acid fumarate have to-date found practical utilization.
Although the aforesaid xe2x80x9cpharmacologically acceptablexe2x80x9d salts solve the problem of the hygroscopicity of L-carnitine inner salt more or less satisfactorily, in none of the known salts the anion moiety co-operates to enhance the nutritional, energetic and/or therapeutical efficacy which can be attributed to the xe2x80x9ccarnitinexe2x80x9d moiety of the salts themselves.
Furthermore, none of the acids used for producing non-hygroscopic L-carnitine salts is capable of forming non-hygroscopic salts of alkanoyl L-carnitine. Thus, for example, whereas L(xe2x88x92)-carnitine acid fumarate and L(xe2x88x92)-carnitine tartrate are non-hygroscopic compounds, acetyl L(xe2x88x92)-carnitine acid fumarate and tartrate, respectively, are strongly hygroscopic compounds, which present the same drawbacks as the corresponding inner salt.
L-carnitine and acyl L-carnitine derivatives with aminoacids are already known.
EP-A1-0 150 688 discloses acetyl L-carnitine acid L-aspartate which is reported as a non-hygroscopic salt.
EP-A2-0 167 115 discloses condensation products of L-carnitine or acyl L-carnitine with an optically active acid aminoacid monosalified with potassium ion. Potassium-salified glutamic and aspartic acids are mentioned and preparation of L-carnitine potassium aspartate is exemplified.
Finally, EP-A1-0 354 848 discloses pharmaceutical compositions comprising L-carnitine lysinate as active ingredient, whose preparation and physico-chemical characterization are not reported.
Neither EP-A2-0 167 115 nor EP-A1-0 354 848 disclose whether the aforesaid L-carnitine derivatives are hygroscopic or non-hygroscopic
The object of the present invention is to provide stable, non-hygroscopic salts of L-carnitine and lower alkanoyl L-carnitine which possess an enhanced therapeutical and/or nutritional efficacy with respect to the corresponding inner salts.
It is, therefore, apparent that the utility of the salts of the present invention is to be found not only in their lack of hygroscopicity and higher stability with respect to their corresponding inner salts, but also insofar as their anion moiety contributes to the nutritional, energetic and/or therapeutic efficacy of the salt as whole. The aforesaid efficacy of these novel salts is, therefore, not to be attributed exclusively to the xe2x80x9ccarnitinexe2x80x9d moiety of the salt.
The aforesaid object, is achieved by the salts of L-carnitine and alkanoyl L-carnitine with amino acids having the formula (I): 
wherein:
R is hydrogen or a straight or branched-chain alkanoyl group having 2-5 carbon atoms; and
Y is the anion of an amino acid occurring in proteins selected from the group consisting of: leucine, isoleucine, vahine, cysteine, arginine, glutamic acid, glutamine, asparagine, glycine, alanine, threonine, serine, proline, hystidine, methionine, phenylalanine and tryptophane.
By xe2x80x9camino acid occurring in proteinsxe2x80x9d is meant any one of the twenty amino acids which are obtained via controlled hydrolysis of naturally occurring proteins (see, e.g., J. David Rawn, Biochemistry, Chapter 3 xe2x80x9cAmino acids and the primary structure of proteinsxe2x80x9d; McGraw-Hill, 1990).
The anion Yxe2x88x92 can optionally be salified at the amino group, preferably with a hydrohalogen acid such as hydrochloric acid or phosphoric acid.
When R is an alkanoyl group, it is preferably selected from the group consisting of acetyl, propionyl, butyryl, valeryl and isovaleryl.
Whilst in order to illustrate the nutritional and therapeutic efficacy of the amino acids in general reference is made to the conspicuously vast literature published to-date on this matter (see, e.g., F. Fidanza and G. Liguori, Nutrizione umana, Chapter 3: xe2x80x9cLe proteinexe2x80x9d, Casa Editrice Libraria Idelson, 1995; and I. Goldberg (Ed.), Functional Foods, Chapter 12, xe2x80x9cAmino acids, peptides and proteinsxe2x80x9d Chapman and Hall, Inc. 1994), it is deemed useful to briefly address the topic of the essential amino acids, in view of their peculiar role, and, among these, of the branched-chain amino acids.
It has long since been known that out of the nine essential amino acids (i.e. those normally occurring in proteins which can not be synthesized by the organism and must therefore be supplemented through the diet), the branched-chain amino acids (BAA) valine, leucine and isoleucine stimulate protein synthesis in skeletal muscle and liver. It is also well known that skeletal muscle is the main site for the initial step in BAAs catabolism resulting in energy production.
With reference to the attached figure which illustrates in a simplified form the relationships between proteins and amino acids within muscle cells, the first metabolic reaction in BAAs oxidative catabolism is transamination, i.e. the transaminase-regulated transfer of an xcex1-amino group resulting in the formation of a branched-chain xcex1-ketoacid (BKA) and a different amino acid. The BKA can either acquire an amino group, thus changing into a BAA again or be further and irreversibly catabolized resulting in energy production. The BKAs are catabolized in this way to a lesser extent within muscle cells. Most of BKAs are exported from muscle via the bloodstream to other organs (such as liver and kidneys) where BKAs are catabolized or re-aminated.
It is well known that strenuous exercise increases BAAs oxidation. In fact, it has been demonstrated that the skeletal musculature of resting well-trained sportsmen oxidizes more BAAs than the musculature of non-trained individuals. It has, furthermore, been shown that the BAAs oxidized by skeletal muscle during physical exercise derive from muscle proteins which are degraded during exercise as well as from the BAAs which are conveyed to the muscle via the bloodstream. The major source of the BAAs delivered via the bloodstream during exercise is the liver.
It is also known that exercise brings about transient periods which extend beyond the exercise, wherein the normal balance of protein synthesis to protein degradation in skeletal muscle has been shifted towards a relative increase in protein degradation. In conclusion, strenuous exercise causes the muscle to use up a portion of its own protein structure.
It has been clearly shown that the quantitative contribution of protein oxidation to the increased energy demand caused by the exercise is relatively small. Nevertheless, BAAs oxidation may be significant insofar as their oxidation generates the amino acids alanine and glutamine which can be exported from muscle to other sites where they are used as energy sources. Alanine is carried via the bloodstream to the liver where it contributes to the formation of glucose, which is the preferred xe2x80x9cfuelxe2x80x9d of the brain, whilst glutamine is an energy source for the kidneys and intestine. It is, therefore, apparent that the increased oxidation of proteins and BAA during exercise is an obligatory event.
One of the functions of BAAs oxidation in the muscle during exercise is the removal of lactate from muscle. In fact, it is well known that the muscle under strenuous exercise burns glucose in a substantially anaerobic manner, resulting in the formulation of lactate which derives directly from pyruvate. Lactate build-up in the muscle is associated with muscle fatigue and onset of muscular cramps and should, therefore, be avoided.
With reference to the figure, the amino groups of BAAs are transferred, via the xcex1-ketoglutarate/glutamate cycle, to pyruvate, resulting in the formation of alanine. Alanine is transferred to the liver where it contributes to glucose synthesis. The pyruvate portion which is involved in alanine synthesis is not converted to lactate. Therefore, BAAs oxidation serves to modulate lactate build-up in skeletal muscle.
Moreover, hydrogen ions from catabolic reactions must be removed, so as to avoid any risk of a pH decrease. Hydrogen ions are removed from muscle by combining (in the form of ammonium ion) with glutamate resulting in glutamine. When taken up by the kidney, ammonium ions (and, hence, hydrogen ions) are extracted with urine.
It is also well known that during strenuous exercise a net loss of BAAs takes place in the liver whilst the skeletal muscle concomitantly takes up BAAs from bloodstream. Therefore, the increased oxidation of BAAs in muscle cells seems to cause a loss in BAAs from liver proteins. It has been further noticed that the rate of protein breakdown in the liver can be partly hindered by amino acids, in particular glutamine. It was in particular noticed that an increased amount of glutamine is exported from liver during exercise which may be related to the effect of this amino acid on protein synthesis.